1. Field of the Invention
This invention relates to display systems and particularly to a television format display system including real time local area histogram equalization.
2. Description of the Prior Art
Histogram equalization of displayed images is a unique image contrast enhancement technique that accumulates and tabulates the occurrences of the intensity of each picture element of a train of video signals to be equalized. Because the amount of information is related to the level of occurrence of each gray scale level, each intensity level in the displayed image does not carry the same amount of information. By utilizing more display gray scale levels at the intensity levels where there are more occurrences of gray scale information in the image and fewer gray scale levels where there are less occurrences the contrast and hence the detail in the displayed image can be greatly improved. The result after truncating of the video to be displayed is that at each gray scale level of the display video an equal number of occurrences of picture elements are provided. Conventionally, histogram equalization has been performed in non-real time by utilizing proper algorithms in a computer. Also it has been known to form histogram equalization with the histogram tabulation developed from the full frame but in this arrangement certain areas such as the dark portions of the image are not suitably enhanced when they are areas or brightness levels that do not have a high level of occurrence in the histogram. A real time histogram equalization system that redistributes the gray levels based on selected and changing portions or local areas of the overall image would provide improved contrast and details in substantially all areas of the picture and would be a substantial advantage to the art.